PermGen and Metaspace

PermGen is an abbreviation for Permanent Generation and it’s a special heap space which is separate from the main Java heap where JVM keeps track of metadata of the classes which have been loaded.

 In Java 8, PermGen has been renamed to Metaspace - with some subtle differences. From our perspective, it is important to note that Metaspace has an unlimited default maximum size.

On the contrary, PermGen from Java 7 and earlier has a default maximum size of 64 MB on 32-bit JVM and 82 MB on the 64-bit version. Of course, these are not the same as the initial sizes.

 Java 7 and earlier starts with something around 12-21 MB of the initial PermGen space.

JVM	Default maximum PermGen size (MB)	Default maximum Metaspace size
32-bit client JVM	64	unlimited
32-bit server JVM	64	unlimited
64-bit JVM	82	unlimited

It is worthwhile to mention that prior to Java 7, interned Strings used to be kept on the PermGen. That caused some serious problems with the infamous:

java.lang.OutOfMemoryError: PermGen space

Whenever there is a need to resize PermGen/Metaspace, JVM will do it as it does with the standard heap. Resizing those spaces requires a full GC, which is always an expensive operation. It can usually be observed during a startup when a lot of classes are being loaded. Especially if the application has dependencies on many external libraries. If there are a lot of full GCs during the startup, it’s usually because of that. If that case, increasing the initial size can boost the startup performance.

To increase PermGen, we have the following commands:

-XX:PermSize=N -  sets the initial (and minimum size) of the Permanent Generation space.

-XX:MaxPermSize=N  -  sets the maximum size of the Permanent Generation space.

In Java 8 and onwards, we can set the initial and maximum size of Metaspace using the following commands:

-XX:MetaspaceSize=N  - sets the initial (and minimum size) of the Metaspace.

-XX:MaxMetaspaceSize=N  - sets the maximum size of the Metaspace.

Examples:

java.lang.OutOfMemoryError: PermGen space

        at java.lang.ClassLoader.defineClass1(Native Method)

        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)

        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)

1. Solution

By default, Tomcat is assigned a very little PermGen memory for the running process. To fix it, increase the PermGen memory settings by using the following Java VM options.

-XX:PermSize<size> - Set initial PermGen Size.

-XX:MaxPermSize<size> - Set the maximum PermGen Size.

2. Windows

Tomcat is managed by this script file catalina.bat, dive inside the script, you will find out that catalina.bat always find and run the setenv.bat file to set the environment variables.

{$tomcat-folder}\bin\catalina.bat

//...

rem Get standard environment variables

if not exist "%CATALINA_BASE%\bin\setenv.bat" goto checkSetenvHome

call "%CATALINA_BASE%\bin\setenv.bat"

goto setenvDone

:checkSetenvHome

if exist "%CATALINA_HOME%\bin\setenv.bat" call "%CATALINA_HOME%\bin\setenv.bat"

:setenvDone

//...

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2.1 To set the environment variable on Windows, create a setenv.bat manually, and put it into the ${tomcat-folder}\bin folder.

${tomcat-folder}\bin\setenv.bat

set JAVA_OPTS=-Dfile.encoding=UTF-8 -Xms128m -Xmx1024m -XX:PermSize=64m -XX:MaxPermSize=256m

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P.S No double quotes, set JAVA_OPTS={value}.

2.2 Restart Tomcat, it will call the setenv.bat file to set the environment variable automatically.

{$tomcat-folder}\bin\catalina.bat restart

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3. Linux

On Linux, the process is same, just Tomcat is using catalina.sh and setenv.sh instead.

3.1 Find out where is catalina.sh :

catalina.sh

$ sudo find / -name "catalina.sh"

Password:

find: /dev/fd/3: Not a directory

find: /dev/fd/4: Not a directory

/Users/mkyong/Downloads/apache-tomcat-6.0.35/bin/catalina.sh

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3.2 Review the catalina.sh, script, it behaves like Windows, but use setenv.sh instead.

//...

# Ensure that any user defined CLASSPATH variables are not used on startup,

# but allow them to be specified in setenv.sh, in rare case when it is needed.

CLASSPATH=

if [ -r "$CATALINA_BASE/bin/setenv.sh" ]; then

  . "$CATALINA_BASE/bin/setenv.sh"

elif [ -r "$CATALINA_HOME/bin/setenv.sh" ]; then

  . "$CATALINA_HOME/bin/setenv.sh"

fi

//...

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3.3 Create a setenv.sh manually, and put it into the ${tomcat-folder}\bin\ folder.

${tomcat-folder}\bin\setenv.sh

export JAVA_OPTS="-Dfile.encoding=UTF-8 -Xms128m -Xmx1024m -XX:PermSize=64m -XX:MaxPermSize=256m"

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P.S With double quotes, export JAVA_OPTS=”{value}”.

3.4 Restart Tomcat.